powerpc/secvar: Warn when PAGE_SIZE is smaller than max object size

Due to sysfs constraints, when writing to a variable, we can only handle
writes of up to PAGE_SIZE.

It's possible that the maximum object size is larger than PAGE_SIZE, in
which case, print a warning on boot so that the user is aware.

Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230210080401.345462-13-ajd@linux.ibm.com

diff --git a/arch/powerpc/kernel/secvar-sysfs.c b/arch/powerpc/kernel/secvar-sysfs.c
index bfb19f2..6ba23b2 100644 (file)
--- a/arch/powerpc/kernel/secvar-sysfs.c
+++ b/arch/powerpc/kernel/secvar-sysfs.c
@@ -225,6 +225,7 @@ static int secvar_sysfs_load_static(void)
 
 static int secvar_sysfs_init(void)
 {
+       u64 max_size;
        int rc;
 
        if (!secvar_ops) {
@@ -274,6 +275,14 @@ static int secvar_sysfs_init(void)
                goto err;
        }
 
+       // Due to sysfs limitations, we will only ever get a write buffer of
+       // up to 1 page in size. Print a warning if this is potentially going
+       // to cause problems, so that the user is aware.
+       secvar_ops->max_size(&max_size);
+       if (max_size > PAGE_SIZE)
+               pr_warn_ratelimited("PAGE_SIZE (%lu) is smaller than maximum object size (%llu), writes are limited to PAGE_SIZE\n",
+                                   PAGE_SIZE, max_size);
+
        return 0;
 err:
        kobject_put(secvar_kobj);